<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>
<script type="text/javascript">

this.m = 15;
function a(m){
	this.m = m;
};
a.prototype = {
	's':function(){
		return this.m + 5;
	}
};
function b(x){
	a.call(this,x);
	/*this.m = 10;*/
};
b.prototype = a.prototype;
alert(new b(this.m).s());

</script>
</body>
</html>